infection and response

• pathogens - microorganisms that can cause disease
• pathogens can spread through

  • air (tiny droplets that we cough or sneeze) eg influenza, measles
  • contaminated food or water eg cholera, salmonella
  • direct contact eg athlete's foot
• how to stop spreading:

  • hygiene washing hands, cleaning cookery items
  • killing vectors eg mosquitos
  • vaccination
  • isolate or quarantine
• Pathogens may be viruses, bacteria, protists or fungi
• Bacteria may produce poisons (toxins) that damage tissues and make us feel ill.
• Bacteria and viruses may reproduce rapidly inside the body.
• Viruses live and reproduce inside cells, causing cell damage
• measles - a viral disease that can be fatal. For this reason, most young children are vaccinated against measles.
• measles symptoms:

  • fever
  • red skin rash
• measles virus is spread by inhalation of droplets from sneezes and coughs
• HIV occurs when the body’s immune system becomes so badly damaged it can no longer deal with other infections or cancers.
• HIV causes flu-like symptoms and can be spread through bodily fluids such as blood which occurs when drug users share needles or sexual contact
• tobacco mosaic virus (TMV) is a widespread plant pathogen affecting many species of plants including tomatoes.
• TMV gives a distinctive ‘mosaic’ pattern of discolouration on the leaves which affects the growth of the plant due to lack of photosynthesis.
• Salmonella food poisoning is spread by bacteria ingested in food, or on food prepared in unhygienic conditions.
• In the UK, poultry are vaccinated against Salmonella to control the spread.
• salmonella symptoms: caused by the bacteria and the toxins they secrete

  • fever
  • abdominal cramps
  • vomiting
  • diarrhoea
• Gonorrhoea is a sexually transmitted disease (STD)
• gonorrhea symptoms:

  • thick yellow or green discharge from the vagina or penis
  • pain urinating
• gonorrhoea is caused by a bacterium and is easily treated with the antibiotic penicillin until many resistant strains appeared
• gonorrhoea is spread by sexual contact and the spread can be controlled by treatment with antibiotics or the use of a barrier method of contraception such as a condom
• rose black spot is a fungal disease where purple or black spots develop on leaves which often turn yellow and drop easily.
• rose black spots affects the growth of the plants as photosynthesis is reduced
• rose black spot is spread in the environment by water or wind.
• rose black spot can be treated by using fungicides and or removing and destroying the affected leaves
• the pathogens that cause malaria are protists
• The malarial protist has a life cycle that includes the mosquito
• Malaria causes recurrent episodes of fever and can be fatal
• The spread of malaria is controlled by preventing the vectors, mosquitos, from breeding and by using mosquito nets to avoid being bitten.
• skin:

  • physical barrier
  • secretes oils/ antimicrobial substances which kill pathogens
  • when skin is broken platelets begin to gather at the site of the wound and a scab forms to maintain the physical barrier
• nose: a physical barrier

  • lots of little hairs to trap dust and dirt
  • mucus that traps pathogens
  • pathogens are removed when a person sneezes
• trachea and bronchi: physical barrier

  • have goblet cells that produce mucus that traps pathogens
  • lined with ciliated cells that have tiny hair called cilia which waft mucus and pathogens towards the stomach
• stomach: chemical barrier

  • pathogens enter the stomach in food or mucus from the trachea and bronchi and get killed by the highly acidic stomach acid ( hydrochloric acid )
• the immune system detects and kills pathogens that have made it past the non-specific defences.
• phagocytes and lymphocytes are types of white blood cells
• White blood cells help to defend against pathogens by:

  • phagocytosis

  • antibody production • antitoxin production.
• phagocytosis:

  • engulf and digest pathogens
  • phagocyte surrounds the pathogens and releases enzymes to digest and break them down to destroy it
  • can be enhanced by antibody production
• production of antibodies:

  • lymphocytes produce antibodies
  • are small proteins which lock up with foreign antigen
  • signals to white blood cells to destroy them
  • antibody is specific to the antigen
  • each lymphocyte only produces one type of antibody
• Memory cells

  Lymphocytes that remain in the body after an initial infection with a particular pathogen
• Memory cells function

  1. Produce the specific antibodies against its antigens

  2. If infected by the same pathogen again in the future (and the antigens are the same), can produce antibodies much quicker against it before its numbers increase and it can cause damage to the tissues of the body